The present invention relates to an apparatus for controlling a plurality of stud tensioning devices.
Stud tensioning devices are used to elongate a stud under tension to allow a nut to rotate thereon. When the tensile stress is subsequently removed, residual tensile stresses remain in the stud, wherein a first member is fastened by the nut to a second member having the stud affixed thereto. The stud tensioning device generally has an air or pneumatic cylinder for gripping the stud, a hydraulic cylinder unit for tensioning the stud, and a motor (such as an air motor) for rotating the nut. Such systems are typically used in nuclear reactor vessels.
Heretofore there has not been any control apparatus proposed in the art for automatically and simultaneously operating a plurality of stud tensioning devices for tensioning studs and rotating nuts thereon for fastening and loosening an upper cover of a nuclear reactor vessel. It has been a general practice in the art to assign a plurality of human operators to manually operate the stud tensioning devices. With reference to FIG. 1A, this manual control method is shown in flowchart form. Note that between each operative step, the pump unit (or supervisors) must monitor the operation and communicate to the operators by way of oral and hand signalling. This greatly increases the stud tensioning operation time. In addition, the operators are exposed to a high amount of radiation and suffer from undue fatigue. Furthermore, the operating costs of this prior art stud tensioning control method are high because a large number of operating steps is involved.